IEEE 802.11, the present standard technique for a wireless LAN, defines two modes as wireless LAN modes. One is an ad hock mode in which a group is formed by wireless nodes (hereinafter also called wireless node apparatuses) which radio waves directly reach to ensure direct communications without intervening a specific base station (hereinafter also called AP (Access Point)), and the other is an infra mode in which an AP is used, and wireless nodes within a range where radio waves from the AP reach (hereinafter also called STA (Station)) are connected to the AP in a star pattern, and can communicate with one another. The use of such a wireless LAN technique can permit wireless nodes to participate in and leave communications in an ad hock manner and execute mobile communications. Those communications however require that radio waves should directly reach a communication destination in ad hock mode, and radio waves should directly reach the AP in infra mode, disabling communications with parties which radio waves cannot directly reach only with wireless links.
The prospect of a wireless LAN is disclosed in Patent Document 1, mentioned below, as a way to speed up mobile communication. A method of constructing a multihop wireless network among wireless nodes is illustrated as one means of widening a service providing area in a system in which the communication area of a base station (AP) is smaller as compared with a mobile communication for a PDC (Personal Digital Cellular) or the like. The invention disclosed in the following patent document aims only at allowing each wireless node to communicate with a base station on a star network so that each wireless node should merely establish a relay path to the base station, and establishes such a configuration that the base station is ranked the highest-rank station among the base station and the wireless nodes and each wireless node specifically determines higher-rank wireless nodes. Further disclosed is a system where the highest-rank station (base station) does not entirely control the establishment of a star multihop wireless network, but the multihop wireless network is autonomously realized as each wireless node selects a higher-rank wireless node with the minimum number of hops to the base station based on the number of hops from the base station, as the optimal wireless node to be connected.
Patent Document 1: Japanese Patent Application Publication No. 2001-237764 (FIG. 1)
In the multihop wireless network having a tree structure with the base station ranked top and each wireless node merely relaying packets received from lower-rank wireless nodes to higher-rank wireless nodes, like the invention disclosed in Patent Document 1, however, packets transmitted from each wireless node are always transferred to the base station, disabling direct communications among wireless nodes. If wireless nodes belonging to the same leaf (wireless node 1001 and wireless node 1002) attempt to communicate with each other on the multihop wireless network as shown in FIG. 10, for example, a base station 1000 should receive packets once, which should be returned into the multihop wireless network. This raises a problem such that not only the delay time is increased, but also bands are used wastefully, thus wasting wireless resources.